SMTPDiag is a great tool. I mentioned it briefly in my last post so I thought I’d give you the run down on how to use it. If someone says “I can’t seem to send an email to this address “and you want to check out resolution information check out SMTPDIAG.SMTPDiag issues DNS queries using both UDP and TCP as mentioned. The first thing it does after of course checking the syntax is to check Start of Authority (SOA) for the remote address domain.
An SOA(State of Authority) Record is the most essential part of a Zone file. The SOA record is a way for the Domain Administrator to give out simple information about the domain like, how often it is updated, when it was last updated, when to check back for more info, what is the admins email address and so on. A Zone file can contain only one SOA Record.
OK the next step is to validate that the local domain MX/A records can be resolved. The test is used to verify that the sender domain is valid and any bounces can be returned to the original server. This test could fail if the domain name is not resolvable from inside the firewall. The remote MX/A records are then also checked. NOTE: If this step fails, mail will not route because of DNS issues, then you know you must check out your DNS infrastructure.
What’s an MX record?
MX stands for Mail Exchange Records. MX records are used in DNS records(or Zone files) to specify how email should be routed. More on MX records here
When all the DNS checks are complete and successfully checked, the tool will try and establish a connection to all the MX records that were published from the remote domain on port 25 and try to EHLO them all, mail from, rcpt to and then the quit command.If you use the verbose (/v) option when you run the tool, more information will be provided about what each test is doing, as well as detailed results of each test step. See my example below.
This is The Usage Syntax: SMTPDIAG “sender address” “recipient address” [-d target DNS] [/v]You will also notice from the results that there is colour coding in the syntax. This means the following:
White text indicates action being taken.
Gray indicates informational results
Green indicates a successful test result.
Red indicates a failed test result.
|sender address||Required. Address of a local mailbox. Used to verify SMTP submission and check inbound DNS.|
|recipient address||Required. E-mail address of remote mailbox you are trying to send mail to. Used to verify DNS, and remote mailbox availability.|
|-d target DNS||Optional. IP address of target DNS server to use to look up remote MX (mail exchange) records for testing. This is often configured as an external DNS server in Exchange. The external DNS setting is not available for Internet Information Services (IIS) SMTP.|
|/v||Optional. Displays additional information about each test.|
I’ve deleted my domain name in this example: Hope this helps!
So download the tool and get testing its the only way to learn…..